|
Physiochemical Behavior of Carbonate Minerals in Soils,
Sediments and Water of Tidal Flats, Northern West part
of Arabian Gulf and Shatt Al-Arab River
Dunia K. Al-Kazaeh
Marine Science Centre, Basrah Univ. Iraq.
Summary
Several thermodynamic parameters are used in order
to estimate the chemical composition and determine the
solubility and stability of various carbonate minerals
that could be found in soils, sediment and water of the
tidal flat of northern-west part of the Arabian Gulf and
Shatt Al-Arab water way, through different equilibrium
experiments, and X- Ray diffraction studies. It was
found that all collected samples have highly carbonate
content and it was ranged between 116 to 440 gm.Kg-1
soil with mean value of 267.31 gm.Kg-1 soil
in all marine location and ranged between 177.5 to 506
gm.Kg-1 soil with mean value of 284.25 gm.Kg-1
soil with alluvial location .Active carbonate content in
all samples were taken a similar trend. Data of X-Ray
diffraction was used to detect carbonate crystalline
minerals in all the studied samples. Results indicate
that the crystalline calcite is present in high content
and ranged from 38% to 70% with the mean value of 57%
from the total carbonate minerals content. The
crystalline dolomite is also detected and ranged from 5
to11% with the mean value of 7.8% from the total
carbonate minerals content. In addition, the studied
samples are also contained Mg-calcite with various
amount of Mg-containing calcite. This means, the calcite
formation in geochemical environment was more rapid than
that of dolomite. Aragonite and magnesium carbonate are
not detected in all
samples.
Results of thermodynamic parameters
showed the following
statements:-
1- The calculated values of ionic
activity products (pIAP) after equilibrium are ranged
between 7.69 to 9.28 with mean value of 8.04 in marine
soils, sediments solution and between 7.78 to 10.02
with mean value of 8.74 in alluvial soil and sediment
solutions, indicating that all the studied sample
solutions are supersaturated with respect of pure
calcite mineral and under saturated with respect of
hydrated calcium carbonate minerals. Lowering values of
ionic activity products than that of solubility products
of aragonite does not mean the presence and controlling
of this mineral in the equilibrium solutions , but the
solutions are saturated with calcite
minerals.
2- Results found that the distribution
coefficient of magnesium ions in calcite minerals
composition was ranged between 0.14 to 14.4% mole MgCO3
in the marine soils and between 0.28 to 13.4% mole MgCO3
in the alluvial soils and sediments, suggesting the
presences various Mg-bearing calcite minerals.
3- Results found that the value of ionic
activity products in all the studied soil and sediments
solutions were under saturated with respect to magnesium
carbonate minerals. This may be due to the replacement
possibility of magnesium ion into calcium sites through
precipitation processes and calcite crystal
growth.
4-The value of ionic activity product (pIAP)
for dolomite mineral was ranged between 15 to 18.28
with mean value of 16.11 in marine soils and sediments
and between 15.38 to 20.12 with mean value of 17.18 in
alluvial soils and sediments. All these values(except
Karmat Ali soil and sediments) were reduced than that of
solubility product of pure dolomite, showing the super
saturation state for dolomite and the (Keq)value
was more than the standard value that is pointing the
calcite- dolomite equilibrium and suggesting the more
stability of dolomite mineral in the most samples of the
study than calcite
mineral.
5-The chemical potential was ranged between
6.14 to 7.64 or between 5.62 to 7.02 in the marine and
alluvial soil and sediments , respectively. This means
that all solution are super saturated with respect to
calcite and aragonite and under saturated with respect
to hydrated calcium carbonate. The intermixture of
magnesium ion in calcite mineral increased the chemical
potential values of calcite .In addition, the chemical
potential of dolomite was ranged between 6.07 to
7.74,indicating the samples were super saturated with
respect to dolomite mineral that controlling the
behavior of calcium and magnesium ion in equilibrium
solutions. Solubility diagram data was agreed with these
conclusions.
6-Almost values of the calculated free energy
of formation for Mg-containing calcite were
increased than that of free energy of formation for
pure calcite and ranged between -268.19 to -270.04
Kcal. mol-1 in marine soil and sediments
and between -269.31 to -272.68 Kcal.mol-1 in
alluvial soil and sediments. These results indicate that
all Mg-containing calcite in the studied soils and
sediments are more soluble and less stable than the
formed and pure
calcite.
7- The calculated results of ionic activity
carbonate minerals showed the super saturated state of
surface and sub- surface marine and river water in
calcite , dolomite and Mg- containing calcite with
0.082-1.11% mole MgCO3 in marine water and
0.092-1.33% mole MgCO3 in river water. There
is not magnesite
formation.
8-Our study is recommended that either Davies&
Jones or Reddy & Nancollass may describe the mechanical
of carbonate minerals precipitation. It is consisted of
suddenly precipitation of calcium carbonate with energy
of 41.66 K.J.mol-1 and the crystal rearrangement to
crystal growth formation . precipitation coefficient
rate for the first stage is more than the second stage
.
Unpublished M.Sc.
Thesis, University of Basrah, 2006
|
